This invention relates to a device incorporating a plurality of members acted upon by a fluid, e.g. blades, vanes, wings or the like, which are fixedly attached to the nave (i.e. hub) of an element forming part of a turbo-machine, such as a propeller, turbine wheel or fan wheel, which members consist of a composite material, the matrix of which consists of a polymer.
It is previously known to produce propellers from reinforced plastic materials. One submarine rescue ship has, for example, been equipped with a shrouded propeller made of polyurethane, reinforced with 25% of long-fibered glass fiber. The production starts with a pre-shaped mat, which is bound by polyvinyl alcohol. The pre-shaped mat is put in a mold whereupon polyurethane is injected in the mould. In this manner has been imitated the stiffness against deformation of bronze propellers, but it has at the same time been obtained a product weighing only one sixth of the weight of a corresponding metallic propeller.
From U.S. Pat. No. 3,883,267 are known turbo-machines, where the blades, wings or vanes consist of a metallic core and a plurality of coating layers of composite fiber material. The metal core has a portion, which is situated outside the blade per se, thus forming the blade attachment root, with the advantages of a metallic attachment, as compared to a plastic attachment. Each of the layers of composite fiber material is so arranged that the angle enclosed between the main direction of a layer and the axis of the blade decreases from a maximum value for the innermost layer or the layers situated closest to the core, to a minimum value for the outermost layer or the layers situated closest to the surface of the blade. It has thereby been tried to counteract the forces caused by mechanical stresses and temperature variations acting in the interface between the metallic core and the composite fiber material.
According to U.S. Pat. No. 3,022,547 blades for turbo-machines, such as compressors or fans, are produced by applying and bonding a plurality of fiber laminates. The fibers of at least a portion of the laminates are inclined in a chordwise direction, forward and aft of a nonradial blade axis, thus forming a biased lay-up with the blade turning center inclined forward or aft of the radial blade axis. This significantly increases the torsional frequency of the blade. In one embodiment, the fibers are inclined in the forward direction such that no fibers extend from the leading blade edge to the blade tip, but, instead, from the leading blade edge to the blade root. This orientation permits the strains to be transmitted to the blade root, where they can be more easily absorbed and dissipated by the blade supporting hub.
The purpose of arranging the fibers in the manner mentioned above is to counteract, as far as possible, the deformation that a propeller made from such a material may be subjected to during service.
Propellers seldom work under uniform and predictable conditions. There are often disturbances and/or altered service conditions, which cause problems, when they concern construction of propellers. These disturbances and changing conditions lead to the fact that the mechanical design of a propeller can not be optimized. The disturbances often lead to particular problems, such as cavitation, vibrations or noise, e.g. during ship propulsion. It is therefor necessary to compromise and to choose the geometry of the propeller so that the propeller can withstand the situations arising. This, however, means that the propeller cannot be given optimum properties. Different steps can be taken to reduce the problems. It is then possible e.g. to take steps aiming to reduce the magnitude of the vibrations, relieve the tip of the propeller blades from load, or to use propellers with tiltable blades, which make it possible to alter the pitch of the blades depending upon the load.
These steps seldom have the desired effect, though they cause extra costs and decreased efficiency and reduced reliability, due to movable parts.